1. Field of the Invention
The present invention relates to a reflection type liquid crystal display.
2. Description of the Prior Art
A number of reflection type liquid crystal displays that create a recognizable image by reflecting incident light originating from the observer""s side have been proposed.
FIG. 1 is a sectional view of a conventional reflection type liquid crystal display.
As shown in FIG. 1, such a conventional reflection type liquid crystal display includes gate electrodes 11 made of a refractory metal, such as chromium (Cr) or molybdenum (Mo), a gate insulating film 12, and active layers 13 made of polysilicon formed successively on an insulating substrate of quartz glass or non-alkali glass or the like.
Each active layer 13 includes channels 13c formed above the gate electrodes 11, and a source 13s and a drain 13d that are formed on both sides of the channels 13c by ion implantation using stopper insulating films 14 on the channels 13c as masks.
An inter-layer insulating film 15, which includes a SiO2 film, a SiN film and a SiO2 film deposited in succession, is formed over the entire surfaces of the gate insulating film 12, the active layer 13 and the stopper insulating films 14. A drain electrode 16 is formed by filling a contact hole, which is formed to correspond to the drain 13d, with a metal, such as Al. Then, a planarization insulating film 17, which consists of an organic resin, for example and serves to flatten the surface, is formed over the entire surface. A contact hole is formed at a location of the planarization insulating film corresponding to the source 13s. A display electrode 19 as a transparent electrode, which consists of ITO (Indium Thin Oxide) in contact with the source 13s through this contact hole and serves also as the source electrode 18, is formed on the planarization insulating film 17. An alignment film 20 consisting of an organic resin, such as polyimide, and aligns liquid crystal elements 21, is formed on the display electrode 19.
A polarizer 40 and a reflector 42 to reflect incident light are arranged on the surface of an insulating substrate having TFTs fabricated as described (a TFT substrate) 10 which is opposite the surface where there is the TFT.
On the side of a counter electrode substrate 30 facing the TFT substrate 10, are provided a color filter 31 including primary colors, red (R), green (G), and blue (B) and a black matrix 32 with a function to shield light; a protective film 33 of a resin formed on the color filter 31; and a counter electrode 34 and an alignment film 35 formed over the entire surface of the protective film 33. On the side not facing the insulating substrate 10, a polarizer 41 is located. The insulating substrate 10 and the counter electrode substrate 30 are bonded together with their peripheries sealed with a sealing bond, thus forming a space inside, and this space is filled with a twisted nematic (TN) liquid crystal 21 with positive dielectric constant anisotropy.
The propagation of light when a user views reflection type liquid crystal display as above is described below with reference to FIG. 1.
As indicated by a broken line with an arrow, an external light 100, such as natural light, coming from outside enters from the polarizer 40 on the side of an observer 101, and passes through the counter electrode substrate 30, the color filter 31, the protective film 33, the counter electrode 34, the alignment film 35, the TN liquid crystal 21, the alignment film 20 on the TFT substrate 10, the display electrode 19, the planarization insulating film 17, the inter-layer insulating film 15, the gate insulating film 12, the glass substrate 10 and the polarizer 40. The light is reflected by the reflector 42, goes through the layers in a direction opposite to the direction of incidence, emerges from the polarizer 41 of the counter electrode substrate 30 and enters the eyes of the observer.
However, after the incident light 100 passes through the display electrode 19a and is reflected by the reflector 42, the reflected light passes between the display electrode 19a and the display electrode 19b and enters the observer""s eyes. More specifically, the fact that the reflected light does not enter to the display electrode 19a gives rise to parallax, and the observer is unable to see an intrinsic image of the display electrode 19a, but rather a disparity. This is a disadvantage.
When a color display is viewed through a color filter as shown in FIG. 1, instead of the proper color of the display electrode, a color disparity due to parallax is viewed.
Another drawback of the conventional reflection type liquid display is that the use of TN liquid crystal results in a very narrow viewing angle for both display and observation.
The present invention has been made to rectify the disadvantages described above and has as its object to provide a reflection type liquid crystal display that offers display without parallax and a wider angle of view.
According to one aspect of the present invention, there is provided a reflection type liquid crystal display, which comprises first and second substrates disposed facing each other and holding a liquid crystal exhibiting a negative dielectric constant anisotropy therebetween; a switching element, a reflective display electrode formed of a conductive reflective material and connected to the switching element, and an alignment film to align the liquid crystal molecules, disposed on the side of the surface of a first substrate facing the second substrate; a counter electrode having an alignment control window for controlling the alignment of the liquid crystal molecules and an alignment film, disposed on the side of a second substrate facing the first substrate; and a phase plate and a polarizer disposed on the side of the second substrate not facing the first substrate.
According to another aspect of the present invention, the reflection type liquid crystal display comprises first and second substrates disposed facing each other and holding therebetween a liquid crystal exhibiting a negative dielectric constant anisotropy; a switching element, a reflective display electrode formed of a conductive reflective material and connected to the switching element, and an alignment film to align the liquid crystal molecules, disposed on the side of the surface of a first substrate facing the second substrate; a counter electrode having an alignment control window for controlling the alignment of the liquid crystal molecules and an alignment film, disposed on the side of a second substrate facing the first substrate; and a phase plate and a polarizer on the side of the second substrate not facing the first substrate, wherein the side of the second substrate not facing the first substrate is viewing side of the display.
According to yet another aspect of the present invention, a light diffusing layer is formed on either one of the sides of the second substrate which faces or does not face the first substrate.
As mentioned above, according to the present invention, the adoption of the reflective display electrodes more effectively reduces the occurrence of parallax by thickness of glass, for example, than when the reflector was provided on the outer side of the TFT substrate.
By the use of a liquid crystal with a negative dielectric constant anisotropy and by the provision of the alignment control windows, it becomes possible to produce a reflection type display with a wider viewing angle for observation from any directionxe2x80x94from above or below or left or right. The addition of the diffusing layer ensures the diffusion of an incident light into the display device or an emerging light from it, so that a bright screen image can be obtained in any direction.
A polarizer used to be mounted in each substrate, but according to the present invention, only one polarizer is mounted. Therefore, because the attenuation of the incident light can be reduced, a brighter image can be obtained.